The role of hormones in fetal lung phospholipid synthesis will be investigated in organ culture. Our previous observation of supra-additive interactions between dexamethasone, theophylline and thyroid hormone will be explored in an attempt to define the mechanism of these interactions. Other studies include investigation of epithelial-mesenchymal interactions in fetal rat lung cultures and pathways of phospholipid synthesis in organotypic cultures of fetal lung.